In recent years, air bags have been widely used as safety measures of automobiles. In particular, one type of air bag has been remarkably spreading which expands or inflates from the front side of an occupant during an impact on an automobile in its longitudinal (front-to-back) direction, so as to absorb shocks when the occupant is thrown toward a front panel or windshield. Subsequently, another type of air bag, called a side impact air bag (or side air bag), has been developed and already used in practice. This type of air bag is adapted to expand from one side of an occupant, to absorb shocks when the occupant is thrown toward a vehicle body or door on the above one side of the occupant.
The side air bag, as described above, is inflated to fill the space between the side body of the automobile and the occupant during the side impact, to absorb shocks between the side body and the occupant. Due to a considerably short distance between the side body and the occupant, this type of air bag is required to deploy with a higher response to a side impact, as compared with the above-described air bag for an impact in the longitudinal direction of the automobile. Also, the side air bag needs to expand toward an appropriate position of the vehicle, to ensure sufficient absorption of shocks on the occupant.
In a structure as disclosed in Japanese laid-open Patent Publication No. 4-50052, for example, a side air bag is provided at a side portion of a seat back, and the position of an inflator including a detonating agent is determined so that the side air bag, when inflated during an impact, is guided in a suitable direction. In this structure, the seat back is formed with an opening through which the side air bag expands outward, and a lid is provided to cover this opening.
In the prior art structure, however, the opening, through which the side air bag expands outward, is normally closed by the lid, and the lid provided on the surface of the seat back is exposed to the outside of the seat, and may deteriorate the appearance of the seat.
Also, the lid is formed of a material that is significantly different in texture from that of a skin or cover of the seat back, which may be formed of a resin material, for example. Thus, the lid cannot be provided on the front face of the seat that makes contact with a body of the occupant, and is consequently provided on the side face of the seat. Accordingly, the opening, through which the side air bag expands outward, is also formed through the side face of the seat back, and the direction of expansion of the side air bag is limited due to the position of the opening.
In view of the above situation, it is desired to provide a structure wherein the side air bag is incorporated within the seat back without using such a lid, so that the side air bag can be appropriately inflated when the vehicle receives an impact.
FIG. 10 is a cross-sectional view showing a known example of a seat for an automobile that is provided with a side air bag, wherein the side air bag is incorporated in the seat back, without providing a lid on a side face of the seat back. This figure shows a cross section as viewed in the direction of arrow A--A in FIG. 9.
As shown in FIG. 9 and FIG. 10, a seat back frame (hereinafter, simply called a "frame") 3 is provided inside a seat back 2 of a seat 1 for an automobile, and an air bag module 11 is attached to this frame 3. While the seat with a side air bag as shown in FIG. 10 is used as a left-side seat of the vehicle, a similar structure symmetrical with this seat may be provided as a right-side seat.
The air bag module 11 includes an inflator 12, and a folded air bag body 13. During an impact on the vehicle, a detonating agent (not shown) explodes, and gas is supplied from the inflator 12 into the air bag body 13, to unfold and inflate the air bag body 13.
During the vehicle impact, a skin 4 of the seat back 2 must be torn to allow the air bag body 13 to expand outwardly of the seat back 2. Further, the air bag body 13 is required to be inflated to fill the space between the side body of the automobile and the occupant to absorb a shock due to a collision between the side body and the occupant. Namely, the air bag body 13 is desired to deploy and expand into an area (inflation area) as indicated by hatched lines in FIG. 10, for example.
In the example shown in FIG. 10, the seat back skin 4 includes a front cloth 4A covering a seating surface on the front side of the seat, a back cloth 4B covering the rear face of the seat back 2, and a side cloth 4C covering each side face of the seat back 2, which cloths 4A, 4B, 4C are sewed together. For example, the air bag body 13 is constructed to expand outwardly of the seat back while rupturing a seam 4D formed between the front cloth 4A and the side cloth 4C.
In the example of FIG. 10 in which the front cloth 4A and side cloth 4C are sewed together, the side cloth 4C itself may be torn before the seam 4D ruptures, depending upon characteristics of the front cloth 4A, if the side cloth 4C is formed of a material that is likely to be torn. As a result, the air bag body 13 may expand out of the seat back 2 in an unexpected or undesirable direction.
If the side cloth 4C is formed of a material that has a tendency of stretching, the side cloth 4C also expands as the air bag body 13 deploys, and it may become difficult for the air bag body 13 to expand, outwardly of the seat back skin 4. Even if the air bag body 13 eventually expands outside the seat back skin 4, it may take a lot of time for the air bag body 13 to fully come out of the seat back, and the side air bag may not be able to exhibit sufficiently high shock-absorbing capability.
To enable the air bag body 13 to expand in a desired direction while rupturing a desired portion of the seat back skin 4, the characteristics (stretch, strength and others) of materials of the seat back skin 4, such as those of the side cloth 4C and front cloth 4A, must be taken into consideration. Also, an air-bag deployment test needs to be conducted each time the material characteristics of the seat back skin 4 are changed, which is time-consuming and results in an increased cost.
In some cases, the air bag body 13 may not expand from a desired location of the seat back skin 4 as expected, depending upon characteristics, such as stretch or strength, of the seat back skin 4. Thus, the material characteristics of the seat back skin 4 are limited, and the range of choices of materials used for the seat back skin 4 is undesirably narrowed.